Variable resistor



June 6, 1961 T. F. KOPACZEK 2,987,688

VARIABLERESISTOR Filed Aug. 1, 1960 FIG. I.

I 3 2)s 34A\fl T n 345 3o lllllllllllllllllll'lll'l a 2B 24 4s 545 A FIG. 2.

FIG. 3.

TED F. KOPACZEK INVEN TOR.

BY i g ATTORNEYS United States Patent 2,987,688 VARIABLE RESISTOR Ted F. Kopaczek, Los Angeles, Calif., assignor to Invar Electronics Corporation, Pasadena, Calif., a corporation of California Filed Aug. 1, 1960, Ser. No. 46,473 1 Claim. (Cl. 338-183) This invention relates to variable resistors and, more particularly, to improvements therein.

A large number of resistors are sold which are required to dissipate substantial amounts of power. These resistors are usually cylindrical in form, effectively comprising a hollow insulating mandrel around which resistance wire is wrapped. An insulator body, such as a ceramic material, covers substantially all but exposed portions of the resistance wire along the length of the mandrel. A contact band, or ring, is mounted over the resistor and is provided with a screw and nut so that the ring may be tightened at any desired location along the resistance for selecting a desired value thereof. Terminal lugs extend from the ends of the resistance wire through the insulating covering. Usually suitable mounting hardware is provided, which effectively requires a screw extending through the hollow mandrel, and a nut mounted thereon to fasten the resistor to the mounting hardware.

The adjustment on the resistor is rather unwieldly. The resistor is usually used in circuits such as power supplies, where substantial voltages exist across the end. To adjust the resistor to a desired value, the screw and nut on the ring must be loosened. The ring is then moved along the resistor and when the desired value is found, it is necessary to hold the ring in place while tightening the screw and nut. To make this adjustment while the voltage is applied across the resistor is hazardous. All insulated tools must be used and a means must be found for holding the ring in place while tightening the screw. To make this adjustment without voltage applied often requires the use of an auxiliary meter. Further, is is oftentimes preferred to make the adjustment while a voltage is applied across the resistor, since this assures that the required value obtained is accurate.

An object of this invention is to provide a simple arrangement for varying the resistance of a resistor of the type described.

Another object of this invention is to provide an arrangement for varying the resistance value of a resistor of the type described without a shock hazard being present, although voltage exists across the resistor.

Yet another object of this invention is the provision of a novel, useful, and approved variable resistor structure for resistors of the type described These and other objects of the invention may be achieved by providing a wire-wound resistor which is mounted on a pair of support members. These support members also carry a threaded leadscrew in parallel with the resistor. A return lead is also supported between the leadscrew and resistor. A slider is threadably engaged with the leadscrew and contacts both return lead and resistor.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a view in elevation of the embodiment of the invention;

FIGURE 2 is a plan view of an embodiment of the invention; and

FIGURE 3 is a cross-sectional view of the embodiment of the invention taken along the lines 33 in FIGURE 2..

Referring now to FIGURES 1 and 2, which show an embodiment of the invention, a resistor 10 of the general type described includes a hollow tubular mandrel body -12, made of an insulating material such as steatite, upon which there is wound resistance wire 15. The ends of the mandrel are permitted to extend beyond the ends of the resistance wire. Ring terminals 16, 18, to which solder connections can be made, clamp the ends of the resistance wire 14 to the mandrel 12. These ring terminals provide the means for making electrical connections to the ends of the resistance wire.

There has been thus far described the usual power resistor without its ceramic coating and without the third movable ring contact mounted on the resistance wire. In accordance with this invention, there is provided a pair of support members 20, 22, each having one end 20A, 22A bent at right angles to the remainder, and a slot formed therein for mounting purposes. A hole 20B, 22B is punched in the body portion of each of the support members and sufiicient material is left around each hole so that the mandrel 12 requires force to be inserted therein. In other words, a force fit is provided between mandrel 12 and support members 20, 22.

Above each of the holes 20B, 22B a slot 20C, 220 is provided in which a return lead 24 is mounted. This return lead or contact bar 24 consists of a fiat piece of Phosphor bronze which has an end twisted to keep it from sliding out of the slot. In each of the support members above the slot opening for the contact bar is another opening 20D, 22D, through which extends a reduced diameter portion of a leadscrew 26. The leadscrew is maintained in position by a pair of tension washers 28, 30. These are bowed to exert spring pressure against the increased diameter threaded portion of the leadscrew. The leadscrew has a slot 32 cut into the headend portion to enable screwdriver rotation of the leadscrew to be made.

A slider for the potentiometer 34 is formed out of a single piece of metal, such as beryllium copper or phosphor bronze. Considering FIGURES 2 and 3, it will be seen that the slider 34 includes what can be called two leadscrew-engaging portions 34A, 34B, which are bent at right angles to and at opposite ends of a base portion 34C. These leadscrew-engaging portions have holes which are slightly larger than the inner diameter of the threaded portion of the leadscrew and radial cuts to enable slight angular displacement of the portions of the material around the leadscrew.

From the remaining opposite ends of the base portion 34C, and bending in a direction opposite to that of the leadscrew-engaging portions, are formed the resistance contact portions 34D, 34E of the slider. These depend on either side of the resistor 10 and are bowed inwardly to apply spring pressure to dimple contacts 34F, 34D, formed in the respective resistance contact portions 34D, 34E. A cutout is made in one of the resistance cutout portions and bent back to form a slide contact 34G and to engage the contact bar 24, which is also in contact with the bottom of the base portion 34C.

Electrical connection with the slider 34 can therefore be made using the end of the contact bar 34 having a terminal aperture. The heavy current which the power dissipating resistor is required to handle is also handled without difiiculty by reason of the double contact made by the slider with both resistor and contact bar, as well as by reason of the size of the contact bar. The support members have potential applied thereto from the contact bar. If it is wished to insulate the assembly from a metal base panel, then insulating sleeves may be employed to slip over or under the mounting portions 20A, 22A to maintain the support members insulated from the underlying metal panel. Preferably, however, these members are made from a block of ceramic material having the required holes drilled therein. The steatite mandrel in such instances is cemented to the ceramic material, rather than force-fitted therein. Also, if desired, the assembly may be mounted on a panel by breaking off the portions 20A, 22A, passing a screw through the mandrel 12 and attaching the assembly to the panel, using a nut or a tapped hole, as desired.

There has accordingly been described and shown herein a novel combination of structures with a power resistor for the purpose of enabling a simple, safe, and more accurate adjustment thereof.

I claim:

The combination with a power resistor of the type wherein resistance wire is wound on a hollow insulating cylindrical mandrel and there are terminals at each end of said wire winding for affording electrical contact therewith, of a pair of elongated support members positioned one at each end of said resistor each having a first pair of openings, each end of said mandrel being force fitted into one of said first pair of openings, each said support member having portions extending in opposite directions from said resistor, the portion extending in one direction away from said resistor terminating in a slotted portion bent at substantially a right angle from the remainder of said support member for affording a mounting base, the portions of said support members extending in the opposite direction from said resistor having a second pair of aligned openings above said first pair of aligned openings, and a third pair of aligned openings above said second pair of aligned openings, a contact bar supported in said second pair of aligned openings, a leadscrew rotatably supported in said third pair of aligned openings and a movable contact, said movable contact having a base portion, first opposite ends of said base portion being bent away therefrom at substantially 90 degrees, aligned apertures in said opposite ends for threadably engaging said leadsc-rew, the remaining opposite ends being bent away from said base portion toward said mandrel to slidably engage said resistance wire at opposite sides of said mandrel, and one of said remaining opposite ends having a cutout portion bent back toward said base portion for slidably engaging said cutout bar.

References Cited in the file of this patent UNITED STATES PATENTS 71,955,906 Crouse Apr. 24, 1934 2 ,870,302 Bourns et al Ian. 20, 1959 2,895,116 Morrison July 14, 1959 

